[Ingress-nginx Security Advisory] CVE-2022-4886: Ingress-nginx `path` sanitization can be bypassed with `log_format` directive

Announcements
1

Issue Details

A security issue was discovered in ingress-nginx where a user that can create or update ingress objects can use directives to bypass the sanitization of the spec.rules[].http.paths[].path field of an Ingress object (in the [networking.k8s.io](http://networking.k8s.io) or extensions API group) to obtain the credentials of the ingress-nginx controller. In the default configuration, that credential has access to all secrets in the cluster.

This issue has been rated High (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H), and assigned CVE-2022-4886.

Affected Components and Configurations

This bug affects ingress-nginx. If you do not have ingress-nginx installed on your cluster, you are not affected. You can check this by running kubectl get po -n ingress-nginx.

If you are running the “chrooted” ingress-nginx controller introduced in v1.2.0 (gcr.io/k8s-staging-ingress-nginx/controller-chroot), command execution is possible but credential extraction is not, so the High severity does not apply.

Multi-tenant environments where non-admin users have permissions to create Ingress objects are most affected by this issue.

Affected Versions- <v1.8.0

Versions allowing mitigation- v1.8.0

Mitigation

Ingress objects contain a field called pathType that defines the proxy behavior. It can be Exact, Prefix and ImplementationSpecific.

When pathType is configured as Exact or Prefix, there is more strict validation, allowing only paths starting with “/” and containing only alphanumeric characters and “-”, “_” and additional “/”.

When this option is enabled, the validation happens in the Admission Webhook, denying creation of any Ingress containing invalid characters (unless pathType is ImplementationSpecific).

https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/configmap/#strict-validate-path-type

Ingress Admins should enable this validation by default. If you still need to allow implementation specific paths due to the usage of features like Regex/rewrite on path, we recommend implementing countermeasures to allow just trusted users to consume this feature, as an example with OPA: https://kubernetes.github.io/ingress-nginx/examples/openpolicyagent/

Detection

If you find evidence that this vulnerability has been exploited, please contact security@kubernetes.io

Additional Details

See ingress-nginx Issue #10570 for more details.

Acknowledgements

This vulnerability was reported by Ginoah, working with the DEVCORE Internship Program.

Thank You,

CJ Cullen on behalf of the Kubernetes Security Response Committee